ajax的python烧瓶示例

Question

For a while now I am trying to learn how to use Ajax with Flask. On the official website of flask there is an example:

from flask import Flask, jsonify, render_template, request
app = Flask(__name__)

@app.route('/_add_numbers')
def add_numbers():
    a = request.args.get('a', 0, type=int)
    b = request.args.get('b', 0, type=int)
    return jsonify(result=a + b)

@app.route('/')
def index():
    return render_template('index.html')

It works for me well. But I am looking for the following program:

1. a jQuery code sends an initial number to the python app
2. the python app stores the number and responds 'received: [the number]'
3. while true: the python app waits for requests 'increase' for which it adds 1 to the number and returns it

The jQuery part doesn't matter, I can do that but I am not sure how to implement the python part:

@app.route('/_inc_number')
def inc_number():
    n = request.args.get('n', 0, type=int)
    while true:
        req = request.args.get('req', 0, type=string)
        if req == 'increase':
            n = n + 1
            return n #It exits the function. how respond without quit?

Please explain me how I can data back? I am new to both Ajax and Flask too, and I suspect that it is not "real" ajax...Is that right? How would you implement a simple function with the same functionality in flask?

Answer 1

HTTP requests don't have a memory, they are independent of each other. It means when your Python app gets a request, it does something, sends a response immediately and quits. That's the nature of HTTP.

If you want something persistent (like your number) that lives through more requests, you need:

• Persistent storage on the server. It can be a file, a database, or in case of Flask simply an object (variable) in memory.
• Identify the user between separate requests. That's what session handling and cookies are for.

A very primitive method (shouldn't be used on production system):

• persistent storage: create a global dict (called num) in main()
• in index():
  • create a random session identifier (si)
  • set num[si] = 0
  • send si as a cookie
• in inc_number() use si from cookie (sent back by the browser) to increase the appropriate num[si]